Fundamental research on the ways voters respond to political campaign advertising can hold great implications for political strategists, architects of campaign finance reform and voting policy, and others. It also can temper claims by commentators, partisans and journalists about the power of specific ads — the idea, for example, that a powerful ad “turned” the election and permanently moved polls. Careful empirical research can inform a more thoughtful discussion of how the public typically reacts to and learns from information.

Recent research has increasingly focused not merely on the immediate effects of mass political communication, but how long the influence, if significant, is likely to last. The relative power of political campaign advertising is the subject of a 2013 study, “How Quickly We Forget: The Duration of Persuasion Effects From Mass Communication,” (working version here) published in Political Communication by authors from the University of California, San Diego, the University of California, Los Angeles, and the University of Mannheim.

To determine how long political campaigning can remain persuasive to voters, the researchers — Seth J. Hill, James Lo, Lynn Vavreck and John Zaller — analyzed data on political advertising effects and candidate preference from the 2000 presidential election as well as the 2006 state and local elections. For the 2000 election, they used a dataset that consists of 12,000 telephone interviews collected by the National Annenberg Election Survey  (NAES) between September 1 and Election Day. The data for the 2006 elections came from the Cooperative Congressional Election Study (CCES), an Internet survey conducted throughout October and November of 2006. These surveys, combined with county-level voting data from the 2000 presidential election, allowed the authors to explore the short and long-term effects of advertising on candidate preference and whether or not this translated into political action.

Key findings from the study include:

• Examining the entire six-week period of data up to Election Day, approximately half of all advertising effects that voters retained in the presidential election came from ads aired during the last week of the campaign. The other half comes from the “surviving effects” of the previous five weeks of advertising. In other words, the final ads of the election were by far the most important.
• Consistent with previous theoretical models, results from the presidential election indicate that “most persuasion effects decay quickly, but that small effects survive six weeks and perhaps longer.”
• In state and local elections, these persuasion effects decay more rapidly: “Advertising causes preference shifts that have half-lives of only 1 to 2 days and no discernible long-term survival.”
• Voters do act under the influence of campaign ads, however, indicating that mass communication retains some political importance, even if the persuasion effects are short-lived.
• While most observed communication effects were “minimal in the particular sense that they are likely to be short-lived,” if political communication is continuously present, “it may also produce a small amount of durable change that, over a long period of time, can add up to a sizable effect.” The authors give examples of this type of constant communication, including ongoing ideological warfare between political parties and wartime propaganda.

The authors note that the findings could have a number of practical implications. The short duration of persuasion effects implies a “limit on the power of money to buy indefinitely large numbers of votes,” which some could find positive, especially given the 2010 Supreme Court ruling in Citizens United v. Federal Election Commission. However, the results could also be seen in a more troubling light: “Political amnesia extends to other political messages that voters would do well to retain.”

For additional reading on the effects of mass communication, see “Counterframing Effects,” a 2013 study on political messaging; “How Large and Long-Lasting Are the Persuasive Effects of Televised Campaign Ads? Results from a Randomized Field Experiment”; and “Dynamic Public Opinion: Communication Effects Over Time.”

Keywords: elections, advertising, mass communication, decay